Absolutely. Without any tests or proofs, they tend to debug the code, then
manually run a few "happy cases" where they know the code will work. This is
nothing to fault them for; they are not professional manual testers, so they
should indeed spend their time developing.

However, if they only write lines of code in response to failing tests, then
the tests will automatically defend not just the happy cases, but all the
cases the team found were important. This, in turn, frees the developer to
focus only on the one feature they are currently adding.

> Testers (when
> available) are notorious for testing to "prove" that the same software
> fails. Who would you rather have design your tests ?

Teams using TDD still have a role for pro testers. They typically work with
the "business analyst" or "customer liaison" roles, to make sure that all
requirements are specified as tests.